Embodiments of the present invention generally relate to routing technologies and more specifically to techniques for supporting asymmetrical adjacency in routers.
In a network, routers form adjacency with peers. Adjacency is formed by exchanging routing information between routers. This forms a two-way relationship in which routers can communicate. Adjacency is typically formed between routers that are considered neighbors, which are routers with interfaces to a common network. Protocols, such as Enhanced Interior Gateway Routing Protocol (EIGRP) define requirements for adjacency. For example, if a router is configured with a static neighbor feature, a static neighbor list defines which routers the router can be adjacent with.
In certain network configurations, such as a hub-and-spoke configuration, a large list of static neighbors is required on the hub because the number of spoke routers may be large, such as in the thousands. This list is manually entered and is hard to maintain.
When a router is configured with the static neighbor feature, all routers that communicate with it should be configured with the same feature. Routers configured with the static neighbor feature are required to send packets using unicast. Thus, a hub router is configured with the static neighbor feature and required to use unicast to communicate with other routers. This may require the hub to send many unicast messages to form adjacency with all the spoke routers.
Also, a router configured with a static neighbor feature is configured to only accept unicast messages because it is expected that all neighbors send messages using unicast. This makes routers configured with the static neighbor feature vulnerable to attacks. For example, an attacker may generate a fake multicast packet that pretends to originate from a router in the network. A router configured with the static neighbor feature considers multicast routers as an incompatible neighbor-type. Thus, adjacency with all other routers may be brought down for the router in this case.